Question

CO relation between work of rivers and work of sea waves

Answer 1

The work of sea water is performed by several marine agents like sea waves, oceanic currents, tidal waves and tsunamis but the sea waves are most pow­erful and effective erosive agent of coastal areas. Sea waves are defined as undulations of sea water charac­terized by well-developed crests and troughs (fig. 20.1). The mechanism of the origin of sea waves is not precisely known but it is commonly believed that waves are generated due to friction on water surface caused by blowing winds.

The undulations of sea water at the place of their origin are called swells which are low, broad, regular and rounded ridges and troughs of water. In other words, ‘the regular pattern of smooth, rounded waves that characterizes the surface of the ocean during fair weather is called swell’.

The height of wind generated sea waves de­pends on:



(i) Wind speed,

(ii) The duration of wind from one direction, and

(iii) The extent of fetch which repre­sents the length of water surface over which the wind blows.

The upper and lower parts of the waves are called wave crests and wave troughs respectively.

The straight horizontal distance between two successive crests or troughs is called wavelength which is ex­pressed in terms of length unit of metres in the case of sea waves. The time taken by a sea wave to cover the distance of one wavelength or wave cycle is called wave period.

The number of sea waves (one sea wave is equal to one wavelength) passing through a certain point per unit time (usually one second) is called wave frequency which varies according to the wavelengths of sea waves. There is inverse relationship between the wavelength and wave frequency i.e., shorter the wave­length, higher the wave frequency